On the pronouns and idiot fascists thread running concurrently, many of the people who posted said they do not have a gender identity – that gender isn’t a component of their identity, that they don’t identify with the gender associated with their sex OR a different gender.
Many nonbinary people describe their own situation in almost exactly the same way. They consider the world to be constructed around “the binary”, i.e., either you’re one of the girls/women or you’re one of the boys/men, and they feel they don’t fit either. That they are agender or neutrois, that gender does not apply to them, they don’t have one.
So if the folks who say they don’t get gender make sense to you, you already understand nonbinary at least in part.
Not all nonbinary people are specifically agender though. It’s another umbrella term, so it covers more than one way of not fitting the either/or of binary gender identities. Other flavors of ninbinary include being genderfluid (people who have boy days and girl days; or who had boy decades but have been having a few decades of being girl since then, or whatever) and also people like me (I’m femme, which is binary, but my sex is male, and the binary assumes your sex and your gender are a matched set; mine are not).